login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A123180 Even positions of Sylvester's sequence A000058; the denominators of the (greedy) Egyptian fraction expansion of Cahen's constant. 2
2, 7, 1807, 10650056950807, 12864938683278671740537145998360961546653259485195807 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

REFERENCES

E. Cahen, (1891). "Note sur un developpement des quantites numeriques, qui presente quelque analogie avec celui en fractions continues". Nouvelles Annales de Mathematiques 10: 508-514.

LINKS

Table of n, a(n) for n=0..4.

Wikipedia, Cahen's constant

FORMULA

a(n) = a(n-1)(a(n-1)-1)(a(n-1)(a(n-1)-1)+1)+1.

a(n) is approximately k^4^n with k = 1.5979102180318731783.... - Charles R Greathouse IV, Dec 12 2013

PROG

(PARI) a(n)=if(n, my(k=a(n-1)); k*=k-1; k*(k+1)+1, 2) \\ Charles R Greathouse IV, Dec 12 2013

CROSSREFS

Cf. A000058, A006279, A006280, A006281, A118227.

Sequence in context: A082891 A000653 A128847 * A138198 A320505 A144836

Adjacent sequences:  A123177 A123178 A123179 * A123181 A123182 A123183

KEYWORD

easy,nonn

AUTHOR

David Eppstein, Oct 03 2006

EXTENSIONS

a(4) from Charles R Greathouse IV, Dec 12 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 10 14:50 EDT 2020. Contains 336381 sequences. (Running on oeis4.)